Introduction to AAM technology : lecture notes of the DuRSAAM training course

(1)

Introduction to AAM technology

Edited by

Stijn Matthys and Alessandro Proia

Lecture notes of the

DuRSAAM training course

held January 2020

(2)

Introduction to AAM technology

Lecture notes of the DuRSAAM training course held January 2020

The PhD Training Network on Durable, Reliable and Sustainable Structures with Alkali-Activated Materials This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 813596 DuRSAAM.

(3)

by Frank Dehn, John Provis, Guang Ye, Stijn Matthys and Alessandro Proia

ISBN 9789082526813 D/2020/15076/01

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (CC BY-NC-SA 4.0). The policy of this license is specified at

https://creativecommons.org/licenses/by-nc-sa/4.0/

This work contains information put forth in the framework of a training course. Reasonable efforts have been made to publish proper information, but the authors and editors cannot assume responsibility for the validity and accuracy of all materials or the consequences of their use. The authors and editors have attempted to avoid any copyright material or to trace the copyright holders and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please contact us via the DuRSAAM web site so that we may rectify in any future version.

Visit DuRSAAM web site at http://www.dursaam.eu

(4)

i | Introduction to AAM technology

Foreword

The design, durability and performance of structures play a crucial role in fostering societal and economic growth. Concrete structures are used extensively for buildings, transport, infrastructure and maritime applications. By using concrete extraordinary structures can be realised, and these are often designed for long service lives to gain optimal value from the material, environmental, intellectual and financial input into the making of the structure.

Although concrete has a fairly limited environmental impact per cubic meter used, concrete is also one of the most frequently used building materials. In Europe, around 4 tonnes of concrete per capita are consumed annually. This makes that concrete is often associated with durability issues and huge environmental costs, for example as the cement industry accounts for about 8% of global anthropogenic carbon dioxide emissions.

There is a clear demand for a new, sustainable generation of construction materials, since Ordinary Portland Cement (OPC)-based concrete cannot meet all the challenges of modern society concerning durability and sustainability. A number of more eco-friendly concrete technologies have appeared over the years, among which a growing interest in concrete technology based on alkali-activated materials (AAM), sometimes also referred to as geopolymers. AAM materials can represent a valuable alternative to OPC for a more sustainable built environment.

This eBook has been made in the framework of the European Training Network on Durable, Reliable and Sustainable Structures with Alkali-Activated Materials (DuRSAAM), which organized a training course on AAM technology held at Karlsruhe Institute of Technology 27- 29 January 2020. This open source book collects the lecture notes by the teachers of this training course and provides building professionals and stakeholders new insights on alkali- activated concrete as an emerging building technology.

Stijn Matthys Alessandro Proia Ghent, 2020

(6)

iii | Introduction to AAM technology

Contributors

Frank Dehn

(Course host, teacher)

Alessandro Proia

(DuRSAAM management assistant) Institute of Concrete Structures and

Building Materials - Materials Testing and Research Institute

Karlsruhe Institute of Technology, Germany

Department of Structural Engineering and Building Materials

Ghent University, Belgium

John Provis

(Course scientific coordinator, teacher)

Stijn Matthys

(DuRSAAM action coordinator) Department of Materials Science and

Engineering

The University of Sheffield, UK

Department of Structural Engineering and Building Materials

Ghent University, Belgium

Guang Ye

(Teacher)

Department Materials, Mechanics, Management & Design

Technical University Delft, The Netherlands

(7)

1 | Introduction to AAM technology – Outline

1. Outline

Stijn Matthys

Concrete is a popular and efficient building material. However, being used that widely all over the world, its environmental impact sums up to large numbers. The upside of this observation is that when improving the environmental impact of concrete, significant improvements can be made in terms of for example reducing carbon dioxide emissions and using less primary raw materials. There are various options to reduce the environmental impact of concrete further, including more efficient cement production, use of recycled aggregates, use of blended cements via secondary cementitious materials and the use of alternative binders. One of these alternative binder technologies is alkali-activated materials (AAM).

The information bundled in this eBook is that of a 3-day course, formatted as a training school open to researchers, practicing engineers, etc., in fact, for all those who want to obtain profound starting knowledge on AAM technology. The original training course, specifically developed and delivered collaboratively by the DuRSAAM action, was held at the Karlsruhe Institute of Technology (KIT), spring 2020. A course introduction video is provided here (time to watch 4 minutes).

The outline of the teaching material bundled in this book, is as follows:

➔ “The cement perspective” (Chapters 2 till 4):

− Cements and the need for improvements

− Alternative solutions, including alkali-activated materials

− Cement characterisation

➔ “The concrete perspective” (Chapters 5 till 7):

− Standardisation of cements and concretes

− Mechanical properties of AAM concretes

− Durability testing of concrete and their applicability to AAM

➔ “Further into the details” (Chapters 8 till 10):

− Modelling of AAM concretes

− Shrinkage of AAM concretes

− Fibre-reinforced AAM concretes

➔ “Hands-on” (Chapter 11):

− AAM lab work

The aim of the teaching material is to impart basic understanding as well as up-to-date knowledge about AAM binders and concretes. The specific learning objectives are as follows:

✓ Understanding about traditional cement versus this new binder technology.

✓ Obtaining insight into the workability, mechanical and durability behaviour of AAM concretes.

✓ Build knowledge on AAM technology and about how these binders and concretes behave compared to traditional hydraulic cements and concretes, respectively.

(8)

✓ Being able to position the emerging AAM technology and its application amongst other construction technologies, and to recognize its value for circular concrete.

In short, for the reader of this eBook to grasp the AAM binder technology for concrete construction.

A brief description of AAM concrete, sometimes also referred to as geopolymer concrete, is given as follows. The composition of traditional concrete and AAM concrete is analogous, as indicated in Figure 1.1. The cement is replaced in AAM concrete by mineral powders (fineness comparable to cement) that will harden by activating these mineral powders with an aqueous solution of alkalis, in contrast to cement that only needs water to harden. Therefore, both concrete types use an alternative chemical route to hydrate into an overall similar artificial rock, based on C(A)SH-like compounds (calcium (alumino)silicate hydrates).

Traditional concrete

Alkali-activated concrete

Figure 1.1 – Composition of traditional versus AAM concrete

The binder component of AAM concrete are mineral powders (called ‘precursors’), which are activated by means of alkalis (called ‘activators). The mineral powders are industrial by- products such as metallurgical slags, combustion ashes and calcined clays, of which some of them have already a tradition to be used as secondary cementitious materials (SCMs) in blended cements. The dosage of these mineral powders, which act as binders instead of cement, is slightly higher than for traditional concrete. As an order of magnitude, the dosage is around 400 kg per m³ of concrete, but depends on the specific mix. Various chemical components can be used for the alkalis, but often a combination of sodium silicate (water glass) and sodium hydroxide is used. The dosage in terms of dry mass of alkalis is, for example, an order of magnitude of 5 mass% with respect to the binder content, for an AAM concrete based on blast furnace slag. The further mix proportioning in terms of fine (sand) and coarse aggregates is the same as with traditional concrete and is performed on the basis of optimal packing distribution. In this respect, is also possible to use recycled or artificial aggregates in AAM concrete. The application of a hybrid solution of concrete with a low dosage of cement and a high dosage of by-products additionally activated, belongs further to the options.

(9)

AAM concrete is compatible with current solutions for reinforcing concrete (reinforcing steel, fibre reinforced concrete,…) and pilot projects with AAM concrete have already been realized in various countries. The characterization and application of AAM concrete is however less advanced than traditional concrete, and the regulatory framework is still limited. Like for traditional reinforced or prestressed concrete, AAM concrete mixes are designed to have good workability, mechanical performance and durability:

• The workability of AAM concrete is generally somewhat more viscous and hardens faster, whereby attention is given in the mix design to obtain a sufficient workable time for the fresh concrete.

• High compressive strengths are generally easy to achieve, but requires attention in the mix design and curing to keep shrinkage deformations under control.

• Due to its generally denser microstructure, AAM concretes have the ability to achieve strong durability properties. On the other hand, the chemical structure of AAM concrete and traditional concrete is not identical, so that further durability tests are recommended to characterize the durability of AAM concrete mixes. In general terms, the durability of AAM concrete is comparable to that of a cement-based concrete, although there might be differences (e.g. carbonation resistance of AAM concrete may be slightly less, resistance to chloride penetration slightly better).

• A common concern of engineers considering AAM concretes for the first time is damage by ASR (alkali-silica reaction). This durability aspect has been examined by various researchers and has not been reported as a problem so far. This is attributed to the fact that alkalis are not freely available in the hardened concrete, but participate in the chemical processes that allow AAM concrete to harden.

In addition to workability, strength and durability, AAM concretes have a lower environmental impact. This is at one hand due to the fact that Portland clinker based cement, with its relatively high environmental impact, is avoided and on the other hand because less primary raw materials are used. The exact gain in environmental impact is not always straightforward to establish, because this depends on (1) the details of the AAM concrete composition, (2) the type of cement based concrete used as a reference for comparison (e.g. concrete based on CEM I or CEM III), and (3) to which extent the environmental impact of the by-products are allocated to its originating production or to the AAM concrete. Under the assumption that mainly the environmental impact of the grinding of the mineral powders is assigned to the AAM concrete and if reference to concrete types with high Portland clinker amounts, values are mentioned of an environmental gain of 50% and more, in terms of carbon footprint.

Furthermore, in terms of end-of-service-life, AAM concrete is recyclable and reusable according to common practices. This has been reported, though studies in this respect are still limited.

By-products for AAM concrete are selected or blended with care, to come to proper mix proportions and to exploit the reactivity of the by-products. It might also be of interest to apply beneficiation treatments on the by-products, to purify them from e.g. valuable metals and to make sure that there is no potential leaching of harmful elements. Environmental permits to use some types of by-products as constituent for concrete might be applicable, depending on national legislation.

(10)

Much more information on AAM binders and concretes, in a wider context of concrete technology, is provided in the following chapters. For further reading on AAMs, also reference is made to the RILEM Handbook “Alkali Activated Materials: State of the Art Report, RILEM TC 224 AAM”, ISBN 978-94-007-7671-5. A link to this handbook is provided here.

(11)

5 | Introduction to AAM technology – Cements and the need for improvement

2. Cements and the need for improvements

John Provis

In this chapter an introduction is given to Portland cement and secondary cementitious materials to create blended cements. The cement hydration is discussed as well as some sustainability considerations with respect to cement usage. The shift from a single universal cement to an array of cement types is highlighted and taken.

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

30 | Introduction to AAM technology – Alternative cements, what is available?

3. Alternative cements, what is available?

John Provis

In this chapter an overview is provided of different alternative cements, including alkali- activated binders. The basics are discussed of a set of 8 non-Portland cements which have been put forth as non-traditional cements.

(37)

(38)

(39)

(40)

(41)

(42)

(43)

(44)

(45)

(46)

(47)

(48)

(49)

(50)

(51)

(52)

(53)

(54)

(55)

(56)

50 | Introduction to AAM technology – Cement characterisation

4. Cement characterisation

John Provis

In this chapter an introduction is provided to the characterisation of cements. Typically a combination of techniques are used to characterize the cement powder by means of experimental testing. Various techniques are discussed in terms of principles of the test method and characterized binder properties.

(57)

(58)

(59)

(60)

(61)

(62)

(63)

(64)

(65)

(66)

(67)

(68)

(69)

(70)

(71)

(72)

(73)

(74)

5. Standardisation of cements and concretes

John Provis

In the construction sector standards and product certification are often applicable. When using novel binder and concrete technologies, existing standards might not always be fully applicable or adapted yet. Nevertheless, though new concrete technologies might be out of scope of existing standards, this does not prevent that they can be already used to some respect. A discussion in this respect is given in this chapter.

(75)

(76)

(77)

(78)

(79)

(80)

(81)

(82)

(83)

(84)

(85)

(86)

80 | Introduction to AAM technology – Mechanical Properties of AAM concretes

6. Mechanical Properties of AAM concretes

Frank Dehn

Given the somewhat different chemical composition of AAM concretes, it is of interest to look into its mechanical performance, and to compare it with relationships provided in existing standards for traditional concrete. This chapter looks into typical strength parameters for concrete, as well as their development over time. Also long-term sustained stress, resulting in creep strains, is discussed.

(87)

(88)

(89)

(90)

(91)

(92)

(93)

(94)

(95)

(96)

(97)

91 | Introduction to AAM technology – Durability testing of concretes

7. Durability testing of concretes

John Provis

In view of the service life of concrete structures, it is important that concretes are made durable. Different durability issues can become apparent in (reinforced) concrete. It is important to also understand how the durability of concrete is tested, so to understand if test methods remain suited to verify the durability behaviour of AAM concrete.

(98)

(99)

(100)

(101)

(102)

(103)

(104)

(105)

(106)

100 | Introduction to AAM technology – Durability testing of concretes

(107)

(108)

(109)

(110)

(111)

(112)

(113)

(114)

108 | Introduction to AAM technology – Modelling of AAM concretes

8. Modelling of AAM concretes

Guang Ye

In this chapter the hydration mechanisms and the resulting microstructure of concrete is considered, looking especially on how to model this. Both Portland cement and alkali-activated materials are considered.

(115)

(116)

(117)

(118)

(119)

(120)

(121)

(122)

(123)

(124)

(125)

(126)

(127)

(128)

(129)

(130)

(131)

(132)

(133)

(134)

(135)

(136)

(137)

(138)

(139)

(140)

(141)

(142)

(143)

(144)

(145)

(146)

(147)

(148)

(149)

(150)

(151)

(152)

(153)

(154)

(155)

(156)

(157)

(158)

(159)

(160)

(161)

(162)

(163)

157 | Introduction to AAM technology – Shrinkage of AAM concretes

9. Shrinkage of AAM concretes

Guang Ye

AAM concrete by nature might sometimes be more sensitive to shrinkage and it is important to consider this in the mix design and curing conditions. In this chapter first a discussion is provided on different forms of shrinkage, how they can be characterized via testing and what can be done to mitigate excessive shrinkage. Secondly, this discussion is continued looking especially into autogenous shrinkage of AAM concrete.

(164)

(165)

(166)

(167)

(168)

(169)

(170)

(171)

(172)

(173)

(174)

(175)

(176)

(177)

(178)

(179)

(180)

(181)

(182)

(183)

(184)

(185)

(186)

(187)

(188)

(189)

(190)

(191)

(192)

(193)

(194)

(195)

(196)

(197)

(198)

(199)

(200)

Introduction to AAM technology : lecture notes of the DuRSAAM training course

Introduction to AAM technology

Stijn Matthys and Alessandro Proia

Lecture notes of the

DuRSAAM training course

held January 2020

Introduction to AAM technology

Lecture notes of the DuRSAAM training course held January 2020

Contents

Foreword

Contributors

Frank Dehn

Alessandro Proia

John Provis

Stijn Matthys

Guang Ye

1. Outline

Stijn Matthys

2. Cements and the need for improvements

John Provis

3. Alternative cements, what is available?

John Provis

4. Cement characterisation

John Provis

5. Standardisation of cements and concretes

John Provis

6. Mechanical Properties of AAM concretes

Frank Dehn

7. Durability testing of concretes

John Provis

8. Modelling of AAM concretes

Guang Ye

9. Shrinkage of AAM concretes

Guang Ye